Exhaust gas after treatment systems are commonly used in conjunction with diesel engines for reducing the amount of nitrous oxides (NOx) in an exhaust gas. One type of after treatment system includes an injector for spraying a reduction agent, such as ammonia, fuel or urea, into the exhaust gas. The exhaust gas is then transported to a catalytic converter where the amount of nitrous oxides in the exhaust gas are reduced as the reduction agent reacts with the nitrous oxides in the exhaust gas to form water and nitrogen. After reacting in the catalytic converter, the exhaust gas is released from the catalytic converter and into the atmosphere.
One problem that may occur with the after treatment system is when the reduction agent leaks out of the after treatment system. In particular, the reduction agent may leak from the after treatment system before reaching the injector. Another problem that may occur with the after treatment system is that the injector may leak the reduction agent from an injection orifice, allowing reduction agent to escape into the exhaust gas. The reduction agent may leak from the injection orifice even when the after treatment system commands the injector not to release the reduction agent into the exhaust gas.